The invention is generally directed to the printing mechanism of a printer and in particular to a printing apparatus for a printer associated with a desktop calculator or an instrument.
In conventional printing mechanisms for serial type printers such the type disclosed in the specification of Japanese Utility Model Laid Open No. 59-122244, an endless belt type carrier (hereinafter referred to as a "type belt") is driven horizontally. A driving cam mechanism and a hammer, which together form a print cam portion and a hammer portion, respectively, for printing a figure, are supported by a hammer holder. The type belt and the cam for urging the hammer against the type belt are controlled by a trigger mechanism including a clutch, an electromagnet and a selection lever. In this type of mechanism, when a desired type element is selected by the trigger mechanism, the type belt is stopped. Then the cam is driven forward, which causes the hammer to be driven, pressing the type against a sheet of paper. After one line of printing is completed the cam portion meshes with a rack supported in the frame to move the printing mechanism to the next column for operation.
When all of the desired figures are printed on a line, the rack is placed out of mesh with the cam portion by a rack removing mechanism and the hammer holder is urged in the direction away from the paper, returning the hammer holder to a home position. The paper feeding is performed in this type of printer by the power produced when the rack is released. Printers of the type described above operate with a type selecting operation, a printing operation and hammer holder return, cam and hammer movement and paper feed operations.
Reference is made to FIG. 25 wherein a printer 100 constructed in accordance with the prior art is depicted. The printer 100 includes an endless belt type carrier 101 with type elements 102 about the outside periphery of belt 101. A head portion 103 including a hammer 104 which is configured to strike the inner surface of endless belt 101 to drive a type element 102 against a sheet of paper 107 supported from behind by a platen 109. The endless belt 101 is driven by a drive gear 105 linked to one of belt support guides 106. A mask 108 provided between the type elements 102 and paper 107 is elastically deformable so that the type elements 102 adjacent to the selected type element 102 do not contact paper 107 when hammer 104 urges the selected type element 102 against paper 107.
In addition, another conventional printer using a type belt is disclosed in the specification of Japanese Utility Model Laid Open No. 59-166954. This printer includes only one space in its symbol type group and printing is achieved by utilizing a carriage with a hammer as described above.
Many types of paper of various widths suitable for use with printers are available on the market. Generally, paper having widths of 38mm and 58mm are conventionally utilized in home desktop calculators and printers utilizing one of these two sizes of papers are generally available. Conventional printers have entirely separate parts, such as paper guides and frame widths prepared for use with a paper of a specific size and thus at least two different printer mechanisms are required to fill the need for printers adapted to take the different widths of paper required in the marketplace.
The prior art endless belt type printers utilize a hammer and a cam mechanism for printing. The cam urges the hammer up into contact with the inside of the endless belt forcing the figure on the type element which is inked to contact the paper thereby printing the figure on the paper. The hammer holder which supports the cam and hammer is moved from column to column and then returned by a mechanism which releases the hammer holder from a rack. As a result, many different parts are required to perform these operations and the overall structure is complicated, making it difficult to manufacture such a printer and resulting in an undesirably high cost of manufacture.
When the conventional printer with an elastic mask, such as mask 108 in FIG. 25, is used, the outside of the type element 102 which is inked, is pressed up against the mask. As a result, the ink is transferred to the mask and then the mask itself is stained with ink. The deformation of the mask by the adjacent type portions on both sides causes the elastic mask to contact the printing paper at the edges. This results in a deterioration in the quality of printing and causes the paper to be stained as the ink leaks around the edges of the mask. In addition, the mask is required to be extremely thin because of the elastic deformation. Thus, the mask can be undesirably deformed during the manufacturing process unless special care is taken which in turn causes the molding of the mask to be expensive and time consuming to attempt to avoid this problem.
In conventional printers a paper guide or frame of the printer is established in accordance with a single paper width. Thus, the printer can only be used with paper of a single width so that there is no interchangeability of paper available.
Accordingly, there is a need for a printer which can be easily constructed with a simple mechanism using fewer parts than the conventional approaches, there is a need for improved printing quality without staining, lower manufacturing costs and mold costs and interchangeability of paper usage by varying a single paper guide in accordance with the width of the paper desired to be used.